Spin transfer magnetic element with free layers having high perpendicular anisotropy and in-plan equilibrium magnetization

ABSTRACT

A method and system for providing a magnetic element that can be used in a magnetic memory is disclosed. The magnetic element includes pinned, nonmagnetic spacer, and free layers. The spacer layer resides between the pinned and free layers. The free layer can be switched using spin transfer when a write current is passed through the magnetic element. The free layer includes a first ferromagnetic layer and a second ferromagnetic layer. The second ferromagnetic layer has a very high perpendicular anisotropy and an out-of-plane demagnetization energy. The very high perpendicular anisotropy energy is greater than the out-of-plane demagnetization energy of the second layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of co-pending U.S. patentapplication Ser. No. 11/239,969, filed on Sep. 30, 2005, which is acontinuation of U.S. patent application Ser. No. 10/789,334, filed onFeb. 26, 2004, issued on Jan. 31, 2006, as U.S. Pat. No. 6,992,359, andincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to magnetic memory systems, and moreparticularly to a method and system for providing a magnetic elementthat employs a spin transfer effect in switching, and that can beswitched using a lower switching current density.

BACKGROUND OF THE INVENTION

FIGS. 1A and 1B depict conventional magnetic elements 10 and 10′. Theconventional magnetic element 10 is a spin valve and includes aconventional antiferromagnetic (AFM) layer 12, a conventional pinnedlayer 14, a conventional conductive spacer layer 16 and a conventionalfree layer 18. Other layers (not shown), such as seed or capping layermay also be used. The conventional pinned layer 14 and the conventionalfree layer 18 are ferromagnetic. Thus, the conventional free layer 18 isdepicted as having a changeable magnetization 19. The conventionalspacer layer 16 is nonmagnetic. The AFM layer 12 is used to fix, or pin,the magnetization of the pinned layer 14 in a particular direction. Themagnetization of the free layer 18 is free to rotate, typically inresponse to an external magnetic field. Also depicted are top contact 20and bottom contact 22 that can be used to drive current through theconventional magnetic element 10. The conventional magnetic element 10′depicted in FIG. 1B is a spin tunneling junction. Portions of theconventional spin tunneling junction 10′ are analogous to theconventional spin valve 10. Thus, the conventional magnetic element 10′includes an AFM layer 12′, a conventional pinned layer 14′, aconventional insulating barrier layer 16′ and a conventional free layer18′ having a changeable magnetization 19′. The conventional barrierlayer 16′ is thin enough for electrons to tunnel through in aconventional spin tunneling junction 10′.

Depending upon the orientations of the magnetization 19/19′ of theconventional free layer 18/18′ and the conventional pinned layer 14/14′,respectively, the resistance of the conventional magnetic element10/10′, respectively, changes. When the magnetization 19/19′ of theconventional free layer 18/18′ is parallel to the magnetization of theconventional pinned layer 14/14′, the resistance of the conventionalmagnetic element 10/10′ is low. When the magnetization 19/19′ of theconventional free layer 18/18′ is antiparallel to the magnetization ofthe conventional pinned layer 14/14′, the resistance of the conventionalmagnetic element 10/10′ is high. To sense the resistance of theconventional magnetic element 10/10′, current is driven through theconventional magnetic element 10/10′. Typically in memory applications,current is driven in a CPP (current perpendicular to the plane)configuration, perpendicular to the layers of conventional magneticelement 10/10′ (up or down, in the z-direction as seen in FIG. 1A or1B).

In addition, films having a perpendicular anisotropy have been used inconventional MRAM to obtain certain desired properties. For example,GdFe and GdCoFe having perpendicular anisotropy have been used inmagnetic elements, as disclosed by Naoki Nishimura, et al. in “Magnetictunnel junction device with perpendicular magnetization films forhigh-density magnetic random access memory”, Journal of Applied Physics,Volume 91, Number 8, pp. 5246-5249, 15 Apr. 2002. However, thestructures disclosed by Nishimura's were designed for standardfield-based-writing MRAM devices. Thus, the magnetization of suchconventional free layers is switched by applying an external magneticfield to the magnetic element. In addition, in contrast to the magneticelements 10/10′, the magnetic elements disclosed by Nishimura have theirequilibrium magnetizations oriented perpendicular to the film plane.Thus, the magnetization of the free layer would be in the z-direction asdepicted in FIGS. 1A and 1B in such conventional magnetic elements.

In order to overcome certain issues associated with magnetic memorieshaving a higher density of memory cells, spin transfer may be utilizedto switch the magnetizations 19/19′ of the conventional free layers10/10′. Spin transfer is described in the context of the conventionalmagnetic element 10′, but is equally applicable to the conventionalmagnetic element 10. Current knowledge of spin transfer is described indetail in the following publications: J. C. Slonczewski, “Current-drivenExcitation of Magnetic Multilayers,” Journal of Magnetism and MagneticMaterials, vol. 159, p. L1 (1996); L. Berger, “Emission of Spin Waves bya Magnetic Multilayer Traversed by a Current,” Phys. Rev. B, vol. 54, p.9353 (1996), and F. J. Albert, J. A. Katine and R. A. Buhrman,“Spin-polarized Current Switching of a Co Thin Film Nanomagnet,” Appl.Phys. Lett., vol. 77, No. 23, p. 3809 (2000). Thus, the followingdescription of the spin transfer phenomenon is based upon currentknowledge and is not intended to limit the scope of the invention.

When a spin-polarized current traverses a magnetic multilayer such asthe spin tunneling junction 10′ in a CPP configuration, a portion of thespin angular momentum of electrons incident on a ferromagnetic layer maybe transferred to the ferromagnetic layer. In particular, electronsincident on the conventional free layer 18′ may transfer a portion oftheir spin angular momentum to the conventional free layer 18′. As aresult, a spin-polarized current can switch the magnetization 19′direction of the conventional free layer 18′ if the current density issufficiently high (approximately 10⁷-10⁸ A/cm²) and the lateraldimensions of the spin tunneling junction are small (approximately lessthan two hundred nanometers). In addition, for spin transfer to be ableto switch the magnetization 19′ direction of the conventional free layer18′, the conventional free layer 18′ should be sufficiently thin, forinstance, preferably less than approximately ten nanometers for Co. Spintransfer based switching of magnetization dominates over other switchingmechanisms and becomes observable when the lateral dimensions of theconventional magnetic element 10/10′ are small, in the range of fewhundred nanometers. Consequently, spin transfer is suitable for higherdensity magnetic memories having smaller magnetic elements 10/10′.

The phenomenon of spin transfer can be used in the CPP configuration asan alternative to or in addition to using an external switching field toswitch the direction of magnetization of the conventional free layer 18′of the conventional spin tunneling junction 10′. For example, themagnetization 19′ of the conventional free layer 18′ can be switchedfrom antiparallel to the magnetization of the conventional pinned layer14′ to parallel to the magnetization of the conventional pinned layer14′. Current is driven from the conventional free layer 18′ to theconventional pinned layer 14′ (conduction electrons traveling from theconventional pinned layer 14′ to the conventional free layer 18′). Themajority electrons traveling from the conventional pinned layer 14′ havetheir spins polarized in the same direction as the magnetization of theconventional pinned layer 14′. These electrons may transfer a sufficientportion of their angular momentum to the conventional free layer 18′ toswitch the magnetization 19′ of the conventional free layer 18′ to beparallel to that of the conventional pinned layer 14′. Alternatively,the magnetization of the free layer 18′ can be switched from a directionparallel to the magnetization of the conventional pinned layer 14′ toantiparallel to the magnetization of the conventional pinned layer 14′.When current is driven from the conventional pinned layer 14′ to theconventional free layer 18′ (conduction electrons traveling in theopposite direction), majority electrons have their spins polarized inthe direction of magnetization of the conventional free layer 18′. Thesemajority electrons are transmitted by the conventional pinned layer 14′.The minority electrons are reflected from the conventional pinned layer14′, return to the conventional free layer 18′ and may transfer asufficient amount of their angular momentum to switch the magnetization19′ of the free layer 18′ antiparallel to that of the conventionalpinned layer 14′.

Although spin transfer functions as a mechanism for switching theconventional magnetic elements 10 and 10′, one of ordinary skill in theart will readily recognize that a high current density is typicallyrequired to induce switching for the conventional magnetic elements 10and 10′. In particular, the switching current density is on the order ofa few 10⁷ A/cm² or greater. Thus, a high write current is used to obtainthe high switching current density. The high operating current leads todesign problems for high density MRAM, such as heating, high powerconsumption, large transistor size, as well as other issues. Moreover,if a spin valve such as the conventional element 10 is used, the outputsignal is small. In the conventional magnetic element 10, both the totalresistance and the change in resistance in SV-based spin transferelements are small typically less than two Ohms and five percent,respectively.

One proposed method of increasing the output signal is to use a spintunneling junction, such as the conventional magnetic element 10′, forthe spin transfer device. The conventional magnetic element 10′ canexhibit large resistance and large signal. For example resistances inexcess of one thousand Ohms and a greater than forty percent percentagechange in resistance, respectively. However, one of ordinary skill inthe art will readily recognize that the use of the conventional magneticelement 10′ requires a small operating current to keep the conventionalmagnetic element 10′ from deteriorating or breaking down.

Accordingly, what is needed is a system and method for providing amagnetic memory element having elements that can be switched using spintransfer at a lower current density and that consume less power. Thepresent invention addresses such a need.

SUMMARY OF THE INVENTION

The present invention provides a method and system for providing amagnetic element that can be used in a magnetic memory. The magneticelement includes pinned, nonmagnetic spacer, and free layers. The spacerlayer resides between the pinned and free layers. The free layer can beswitched using spin transfer when a write current is passed through themagnetic element. The free layer includes a first ferromagnetic layerand a second ferromagnetic layer. The second ferromagnetic layer has avery high perpendicular anisotropy and an out-of-plane demagnetizationenergy. The very high perpendicular anisotropy energy is greater thanthe out-of-plane demagnetization energy of the second layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a conventional magnetic element, a spin valve.

FIG. 1B is a diagram of another conventional magnetic element, a spintunneling junction.

FIG. 2A depicts a first embodiment of a portion of a magnetic element inaccordance with the present invention having a reduced write currentdensity for spin transfer switching.

FIG. 2B depicts another version of the first embodiment of a portion ofa magnetic element in accordance with the present invention having areduced write current density for spin transfer switching.

FIG. 3A depicts a second version of the first embodiment of a portion ofa magnetic element in accordance with the present invention having areduced write current density for spin transfer switching due to atleast a high perpendicular anisotropy.

FIG. 3B depicts a third version of the first embodiment of a portion ofa magnetic element in accordance with the present invention having areduced write current density for spin transfer switching due to atleast a high perpendicular anisotropy.

FIG. 4 depicts a second embodiment of a magnetic element in accordancewith the present invention having a reduced write current density forspin transfer switching.

FIG. 5A is a preferred version of the second embodiment of a magneticelement in accordance with the present invention having a reduced writecurrent density for spin transfer switching.

FIG. 5B depicts a second version of the second embodiment of a portionof a magnetic element in accordance with the present invention having areduced write current density for spin transfer switching due to highperpendicular an isotropy.

FIG. 5C depicts a third version of the second embodiment of a portion ofa magnetic element in accordance with the present invention having areduced write current density for spin transfer switching due to highperpendicular an isotropy.

FIG. 6 depicts a third embodiment of a portion of a magnetic element inaccordance with the present invention having a reduced write currentdensity for spin transfer switching.

FIG. 7A is a preferred version of the third embodiment of a magneticelement in accordance with the present invention having a reduced writecurrent density for spin transfer switching.

FIG. 7B depicts another version of the third embodiment of a portion ofa magnetic element in accordance with the present invention having areduced write current density for spin transfer switching due to atleast high perpendicular an isotropy.

FIG. 7C depicts another version of the third embodiment of a portion ofa magnetic element in accordance with the present invention having areduced write current density for spin transfer switching due to atleast high perpendicular an isotropy.

FIG. 8 depicts a flow chart of a one embodiment of a method inaccordance with the present invention for providing one embodiment of amagnetic element in accordance with the present invention having areduced write current density for spin transfer switching.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an improvement in magnetic elements andmagnetic memories, such as MRAM. The following description is presentedto enable one of ordinary skill in the art to make and use the inventionand is provided in the context of a patent application and itsrequirements. Various modifications to the preferred embodiments will bereadily apparent to those skilled in the art and the generic principlesherein may be applied to other embodiments. Thus, the present inventionis not intended to be limited to the embodiments shown, but is to beaccorded the widest scope consistent with the principles and featuresdescribed herein.

The present invention provides a method and system for providing amagnetic element that can be used in a magnetic memory. The magneticelement comprises at least pinned, nonmagnetic spacer, and free layers.The spacer layer resides between the pinned and free layers. Themagnetic element is configured to allow the free layer to be switchedusing spin transfer when a write current is passed through the magneticelement. In some aspects, the magnetic element further comprises abarrier layer, a second pinned layer. In other aspects, the magneticelement further comprises a second spacer layer, a second pinned layerand a second free layer magnetostatically coupled to the first freelayer. In such an aspect, the second spacer layer is between the secondpinned and second free layers and a separation layer is preferablyprovided between the first and second free layers to ensure they aremagnetostatically coupled. In one aspect, one or more of the free layershas a perpendicular anisotropy. The perpendicular anisotropy has aperpendicular anisotropy energy at least twenty percent and, in general,less than one hundred percent of the out-of-plane demagnetizationenergy.

The present invention will be described in terms of a particularmagnetic memory and a particular magnetic element having certaincomponents. However, one of ordinary skill in the art will readilyrecognize that this method and system will operate effectively for othermagnetic memory elements having different and/or additional componentsand/or other magnetic memories having different and/or other featuresnot inconsistent with the present invention. The present invention isalso described in the context of current understanding of the spintransfer phenomenon. Consequently, one of ordinary skill in the art willreadily recognize that theoretical explanations of the behavior of themethod and system are made based upon this current understanding of spintransfer. One of ordinary skill in the art will also readily recognizethat the method and system are described in the context of a structurehaving a particular relationship to the substrate. For example, asdepicted in the drawings, the bottoms of the structures are typicallycloser to an underlying substrate than the tops of the structures.However, one of ordinary skill in the art will readily recognize thatthe method and system are consistent with other structures havingdifferent relationships to the substrate. In addition, the method andsystem are described in the context of certain layers being syntheticand/or simple. However, one of ordinary skill in the art will readilyrecognize that the layers could have another structure. For example,although the method and system are described in the context of simplefree layers, nothing prevents the present invention from being used withsynthetic free layers. Furthermore, the present invention is describedin the context of magnetic elements having particular layers. However,one of ordinary skill in the art will readily recognize that magneticelements having additional and/or different layers not inconsistent withthe present invention could also be used. Moreover, certain componentsare described as being ferromagnetic. However, as used herein, the termferromagnetic could include ferrimagnetic or like structures. Thus, asused herein, the term “ferromagnetic” includes, but is not limited toferromagnets and ferrimagnets. The present invention is also describedin the context of single elements. However, one of ordinary skill in theart will readily recognize that the present invention is consistent withthe use of magnetic memories having multiple elements, bit lines, andword lines. The present invention is also described in the context of aparticular mechanism, a high anisotropy, for providing a lower switchingcurrent density. However, one of ordinary skill in the art will readilyrecognize that the method and system described herein can be combinedwith other mechanisms for reducing the switching current density, suchas a low saturation magnetization free layer.

To more particularly illustrate the method and system in accordance withthe present invention, refer now to FIG. 2A, depicting a firstembodiment of a portion of a magnetic element 100 in accordance with thepresent invention having a reduced write current density for spintransfer. The magnetic element 100 is preferably used in a magneticmemory, such as a MRAM. Thus, the magnetic element 100 may be used in amemory cell including an isolation transistor (not shown), as well asother configurations of magnetic memories. Moreover, the magneticelement 100 preferably utilizes two terminals (not shown) near the topand bottom of the magnetic element. However, nothing prevents the use ofanother number of terminals, for example a third terminal near thecenter of the magnetic element. The magnetic element 100 includes apinned layer 110, a spacer layer 120, and a free layer 130. As describedbelow, the free layer 130 is configured to have a high perpendicularanisotropy. The magnetic element 100 generally also includes an AFMlayer (not shown) used to pin the magnetization 111 of the pinned layer110, as well as seed layers (not shown) and capping layers (not shown).Furthermore, the magnetic element 100 is configured such that the freelayer 130 can be written using spin transfer. In a preferred embodiment,the lateral dimensions, such as the width w, of the free layer 130 arethus small and preferably less than two hundred nanometers. In addition,some difference is preferably provided between the lateral dimensions toensure that the free layer 130 has a particular easy axis in the planeof the free layer 130.

The pinned layer 110 is ferromagnetic. In one embodiment the pinnedlayer 110 is synthetic. In such an embodiment, the pinned layer 110includes ferromagnetic layers separated by nonmagnetic layers and isconfigured such that the ferromagnetic layers are aligned antiparallel.The pinned layer 110 may be configured to increase the spin dependenceof the bulk resistivity of the magnetic element 100. For example, thepinned layer 110, or its ferromagnetic layers, may be a multilayer madeup of repeated bilayers (not explicitly shown in FIG. 2A). In one suchembodiment, the pinned layer 110 could be a multilayer of(Fe_(x)Co_(1-x)/Cu)n, where n is the number of times theFe_(x)Co_(1-x)/Cu bilayer is repeated. In such embodiment, n is greaterthan one and the Cu layer of the bilayer is preferably one through eightAngstroms thick. The spacer layer 120 is nonmagnetic. In one embodiment,the spacer layer 120 may be conductive, for example including Cu. Inanother embodiment, the spacer layer 120 is a barrier layer including aninsulator such as alumina. In such an embodiment, the barrier layer 120is less than two nanometers thick such that charge carriers can tunnelbetween the free layer 130 and the pinned layer 110.

The free layer 130 is ferromagnetic and is configured to have a highperpendicular anisotropy. As used herein, a high perpendicularanisotropy occurs for the simple free layer 130 when the perpendicularanisotropy of the free layer 130 has a corresponding perpendicularanisotropy energy that is at least twenty percent and less than onehundred percent of the demagnetization energy. FIG. 2B depicts amagnetic element 100′ that is analogous to the magnetic element 100.Thus, analogous components are labeled similarly. The magnetic element100′, therefore, includes a free layer 130′ that can be written usingspin transfer and that has a high perpendicular anisotropy. However, thefree layer 130′ is synthetic, including two ferromagnetic layers 132 and136 separated by a nonmagnetic layer 134 that is preferably Ru. Thenonmagnetic layer 134 is configured so that the magnetizations 133 and137 of the free layer 130′ are aligned antiparallel. The free layer 130′has a high perpendicular anisotropy because the ferromagnetic layers 132and 136 have a high perpendicular anisotropy. Thus, the perpendicularanisotropy of the ferromagnetic layers 132 and 136 corresponds to aperpendicular anisotropy energy that is at least twenty percent and lessthan one hundred percent of the demagnetization energy of theferromagnetic layers 132 and 136, respectively. Referring to FIGS. 2Aand 2B, the high perpendicular anisotropy is defined to have aperpendicular anisotropy energy that is at least twenty percent but lessthan one hundred percent of the demagnetization energy. Consequently,although the perpendicular anisotropy is substantial, the equilibriummagnetization of the free layer 130 or the constituent ferromagneticlayers 132 and 136 lie in plane (no components up or down in FIGS. 2Aand 2B). For clarity, the discussion below primarily refers to the freelayer 130. However, the principles discussed also apply to the freelayer 130′, including ferromagnetic layers 132 and 136, and the magneticelement 100′.

A high perpendicular anisotropy occurs when the perpendicular anisotropyenergy of the free layer 130 is greater than twenty percent but lessthan one hundred percent of the out-of-plane demagnetization energy ofthe free layer 130. As a result, the magnetization 131 of the free layer130 lies in plane at equilibrium (in the absence of a write current or asufficient external magnetic field). The high perpendicular anisotropyis preferably provided using materials having a high perpendicularcrystalline anisotropy and/or by stressing the layer in some manner. Thehigh perpendicular anisotropy should reduce the critical switchingcurrent density, J_(c), required to switch the magnetization of the freelayer 130 due to spin transfer.

The ability of the high perpendicular anisotropy free layer to reducethe switching current density can be understood using the prevalent spintransfer spin-torque model described in J. C. Slonczewski,“Current-driven Excitation of Magnetic Multilayers,” Journal ofMagnetism and Magnetic Materials, vol. 159, p. L1-L5 (1996). Accordingto Slonczewski's model, the switching current density Jc for the freelayer of a spin transfer stack is proportional to:

αtM_(s)[H_(eff)−2πM_(s)]/g(θ)

where:

α=the phenomenological Gilbert damping constant;

t=the thickness of the free layer;

M_(s)=saturation magnetization of the free layer;

H_(eff)=effective field for the free layer;

g(θ) reflects the spin-transfer efficiency

The effective field, H_(eff), includes the external magnetic field,shape anisotropy fields, in-plane and out-of-plane (i.e. perpendicular)anisotropies, and dipolar and exchange fields. The perpendicularanisotropy typically arises from crystalline anisotropy. The term g(θ)depends on the relative angular orientations of the magnetizations ofthe pinned layer 110 and the free layer 130.

The ability of a high perpendicular anisotropy to reduce the switchingcurrent density can be explained as follows. For the majority ofmagnetic materials, the out-of-plane demagnetization term 2πM_(s) ismuch greater than H_(eff). For instance, for a thin film ellipse of Cowith the majority axis of 200 nm, minority axis of 100 nm, and thicknessof 20 A, the term 2πM_(s) is approximately 8 kOe, which is much largerthan H_(eff) that is less than a few hundred Oe. A high perpendicularanisotropy, generally a crystalline anisotropy, can be introduced intothe free layer 130 to offset most, but not all, of the out-of-planedemagnetization. Thus, as defined above, the high perpendicularanisotropy has a perpendicular anisotropy energy that is less than onehundred percent of the demagnetization energy. The high perpendicularanisotropy has a perpendicular anisotropy energy that is preferablybetween twenty and ninety five percent (and in a preferred embodiment,is ninety percent) of the demagnetization energy. Because theout-of-plane demagnetization energy would then be still larger than theperpendicular anisotropy energy, the equilibrium magnetization 131 ofthe free layer 130 should remain in-plane. However, because theperpendicular anisotropy has been greatly increased, the differencebetween the effective field H_(eff) (which includes the perpendicularanisotropy), and the demagnetization term 2πM_(s), is decreased. Thus,the equilibrium magnetic moment of the free layer 130 remains in plane,but can be switched using a lower switching current density. In short,to reduce the switching current density for a spin transfer inducedswitching of the magnetization 131 of the free layer 130, a highperpendicular anisotropy should be provided for the free layer 130.

The high perpendicular anisotropy for the free layer 130 can be providedin a number of ways. In order to provide a high perpendicularanisotropy, materials used in the free layer 130, or the constituentferromagnetic layers 132 and 136, could include materials having a highperpendicular anisotropy due to their crystal structure. In oneembodiment, the free layer 130 or the ferromagnetic layers 132 and 134include Co and CoFe; or Co and CoFe alloyed with Cr, Pt, and/or Pd wherethe compositions of Cr, Pt, and Pd are chosen to give high perpendicularanisotropy, as defined above. In a preferred embodiment, thecompositions of Cr, Pt, and/or Pd in Co and CoFe are adjusted to satisfythe condition that the perpendicular anisotropy energy is between twentyand ninety five percent, and preferably ninety percent, of theout-of-plane demagnetization energy.

In an alternative embodiment, the free layer 130 or the ferromagneticlayers 132 and 134 can include multilayers [Co/Pd]n/Co, [Co/Pt]n/Co,[CoFe/Pd]n/CoFe, [CoFe/Pt]n/CoFe, [CoCr/Pd]n/CoCr, or [CoCr/Pt]n/CoCrwhere n is between 1 and 10, Co 3 A to 20 A, CoFe 3 A to 20 A, CoCr 3 Ato 20 A, Pd 10 A to 100 A, Pt 10 A to 100 A. The exact thicknesses ofCo, CoFe, CoCr, Pd, and Pt are chosen so that the perpendicularanisotropy energy is between twenty and ninety five percent of theout-of-plane demagnetization energy of the multilayers. Theperpendicular anisotropy in these multilayers is attributed to surfaceanisotropy at the ferromagnetic/Pd or Pt interfaces and to the strain inthin Co layers.

FIG. 3A depicts another version 100″ of the first embodiment of aportion of a magnetic element in accordance with the present inventionhaving a reduced write current density for spin transfer switching. Themagnetic element 100″ is analogous to the magnetic element 100. Thus,analogous components are labeled similarly. Therefore, the magneticelement includes a free layer 130″ that has a high perpendicularanisotropy and which is written using spin transfer. Moreover, themagnetic element 100″ preferably utilizes two terminals (not shown) nearthe top and bottom of the magnetic element. However, nothing preventsthe use of another number of terminals, for example a third terminalnear the center of the magnetic element. In a preferred embodiment, thefree layer 130″ includes Co, CoCr, CoPt, CoCrPt, CoFe, CoFeCr, CoFePt,CoFeCrPt, or their multilayer combinations, which have an intrinsic highperpendicular anisotropy. The magnetic element 100″ also includesoptional stress increasing layers 152 and 154. One or both of the stressincreasing layers 152 and 154 may be used. The layer 154 is used toalter the stress and the surface anisotropy of the free layer 130″,leading to further enhancement of the total perpendicular anisotropy.The stress increasing layer 152 is a seed layer that also enhances thetotal perpendicular anisotropy of the free layer 130″. The stressincreasing layer 152 may act as part of the spacer layer 120″ when thespacer layer 120″ is conductive. However, if the spacer layer 120″ is aninsulating barrier layer, the inclusion of the stress increasing layer152 can cause a significant degradation in signal. In such anembodiment, the stress increasing layer 152 is, therefore, undesirable.The stress increasing layers 152 and 154 may include a few Angstroms ofmaterials such as Pt, Pd, Cr, Ta, Au, and Cu that further promoteperpendicular anisotropy in the free layer 130″. However, note that theuse of Pt and Pd either within the free layer 130″ or adjacent layers152 and 154 could increase the phenomenological Gilbert dampingconstant, α. An increase in α could negate some or all of the switchingcurrent density reduction brought about by high perpendicular anisotropyin the free layer 130″. In addition, the perpendicular anisotropy of thematerials above, such as Co, CoCr, CoPt, CoCrPt, CoFe, CoFeCr, CoFePt,and CoFeCrPt, can be further increased by intrinsic stress in the filmitself. This intrinsic stress may be induced during the film depositionand/or by surrounding the spin transfer stack (containing the free layer130″) with an insulator (dielectric) of high compressive stress.

FIG. 3B depicts another version 100′″ of the first embodiment of aportion of a magnetic element in accordance with the present inventionhaving a reduced write current density for spin transfer. The magneticelement 100′″ is analogous to the magnetic element 100. Therefore, themagnetic element 100′″ includes a free layer 130′″ that has a highperpendicular anisotropy, an optional low saturation magnetization, andwhich is written using spin transfer. Moreover, the magnetic element100′″ preferably utilizes two terminals (not shown) near the top andbottom of the magnetic element. However, nothing prevents the use ofanother number of terminals, for example a third terminal near thecenter of the magnetic element.

The free layer 130′″ has a high perpendicular anisotropy, as definedabove. The free layer 130′″ also includes a very high perpendicularanisotropy ferromagnetic layer 160 and a ferromagnetic layer 162. In apreferred embodiment, the high perpendicular anisotropy of the freelayer 130′″ is provided at least in part due to the very highperpendicular anisotropy ferromagnetic layer 160. The very highperpendicular anisotropy ferromagnetic layer 160 has a very highperpendicular anisotropy. As used herein, a very high perpendicularanisotropy has a perpendicular anisotropy energy that exceeds theout-of-plane demagnetization energy. As a result, a film having a veryhigh perpendicular anisotropy, when standing alone, would have itsequilibrium magnetization perpendicular to the plane. The very highperpendicular anisotropy ferromagnetic layer 160 is preferably a rareearth-transition metal alloy, such as GdFe and GdCoFe, where the rareearth may be in the range of five to sixty atomic percent. Such rareearth-transition metal alloys have relatively low damping constants andhigh or very high perpendicular anisotropy. The very high perpendicularanisotropy ferromagnetic layer 160 preferably has a perpendicularanisotropy energy larger than its own out-of-plane demagnetizationenergy. The ferromagnetic layer 162 has a high spin polarization. Thus,the ferromagnetic layer 162 preferably includes one or more highspin-polarization materials such as Co, Fe, or CoFe. The ferromagneticlayer 162 has a perpendicular anisotropy energy that is smaller than itsout-of-plane demagnetization energy. The very high perpendicularanisotropy ferromagnetic layer 160 and the ferromagnetic layer 162 areexchange-coupled.

The exchange-coupled combination of the very high perpendicularanisotropy sublayer 160 and the high spin polarization ferromagneticlayer provide a total high perpendicular anisotropy for the free layer130′″. At larger thickness of the very high perpendicular anisotropyferromagnetic layer 160, the total perpendicular anisotropy energy ofthe combination of the very high perpendicular anisotropy ferromagneticlayer 160 and the ferromagnetic layer 162 exceeds the total out-of-planedemagnetization energy for the very high perpendicular anisotropyferromagnetic layer 160 and the ferromagnetic layer 162. In such a case,the magnetizations of both the very high perpendicular anisotropyferromagnetic layer 160, the ferromagnetic layer 162 and thus the freelayer 130′″ would be oriented perpendicular to the film plane. If thethickness of the very high perpendicular anisotropy ferromagnetic layer160 is reduced, however, the total perpendicular anisotropy energy ofthe very high perpendicular anisotropy ferromagnetic layer 160 and theferromagnetic layer 162 is reduced faster than the total out-of-planedemagnetization energy of the very high perpendicular anisotropyferromagnetic layer 160 and the ferromagnetic layer 162. Stateddifferently, the total perpendicular anisotropy energy of the free layer130′″ is reduced more rapidly than the total out-of-planedemagnetization energy of the free layer 130′″. Alternatively, if thethickness of the high spin-polarization ferromagnetic 162 is increased,the total perpendicular anisotropy energy of the very high perpendicularanisotropy ferromagnetic layer 160 and the ferromagnetic layer 162 isincreased more slowly than the total out-of-plane demagnetization energyof the very high perpendicular anisotropy ferromagnetic layer 160 andthe ferromagnetic layer 162. Stated differently, the total perpendicularanisotropy energy of the free layer 130′″ is increased more slowly thanthe out-of-plane demagnetization energy of the free layer 130′″. Whenthe total perpendicular anisotropy energy becomes less than the totalout-of-plane demagnetization energy, the equilibrium magnetizations ofthe very high perpendicular anisotropy ferromagnetic layer 160 and theferromagnetic layer 162 rotate into the film plane. Stated differently,the perpendicular anisotropy energy of the free layer 130′″ is less thanthe out-of-plane demagnetization energy of the free layer 130′″ and themagnetization of the free layer 130′″ is in plane even though the freelayer 130′″ has a high perpendicular anisotropy. Thus, to decrease thespin-transfer switching current, the thicknesses of the very highperpendicular anisotropy ferromagnetic layer 160 and the ferromagneticlayer 162 are tailored such that the total perpendicular crystallineanisotropy is high. Stated differently, the perpendicular anisotropy ofthe combination of the layers 160 and 162 has a perpendicular anisotropyenergy that is at least twenty and less than one hundred percent of thedemagnetization energy. In a preferred embodiment, this anisotropyenergy is ninety percent of the total out-of-plane demagnetizationenergy. For example, in one embodiment, the magnetic element 100′″ couldbe a top MTJ, having the free layer 130′″ at the bottom closest to thesubstrate, the spacer or barrier layer 120′″ and a pinned layer 110′″ atthe top. Such a magnetic element would include: very high perpendicularanisotropy ferromagnetic layer 160/ferromagnetic layer 162/spacer(barrier) layer 120′″/pinned layer 110′″/pinning or AFM layer (notshown). Thus, an example of the magnetic element 100′″ is given by:AlCu[250 A]/GdFeCo[t]/CoFe[10 A]/Al2O3[8 A]/CoFe[30 A]/PtMn[150 A],where the thickness, t, of GdFeCo is preferably adjusted between ten andfour hundred Angstroms so that the that the total perpendicularcrystalline anisotropy energy is between at least twenty and less thanone hundred percent, preferably ninety percent, of the totalout-of-plane demagnetization energy. Thus, the equilibrium magneticmoment of the free layer 130′″ should remain in-plane.

In an alternative embodiment, the very high perpendicular anisotropyferromagnetic layer 160 can include multilayers [Co/Pd]n/Co,[Co/Pt]n/Co, [CoFe/Pd]n/CoFe, [CoFe/Pt]n/CoFe, [CoCr/Pd]n/CoCr, or[CoCr/Pt]n/CoCr where n is between 1 and 10, Co 3 A to 20 A, CoFe 3 A to20 A, CoCr 3 A to 20 A, Pd 10 A to 100 A, Pt 10 A to 100 A. The repeatnumber n and the exact thicknesses of Co, CoFe, CoCr, Pd, and Pt arechosen so that the total perpendicular anisotropy energy is betweentwenty and ninety five percent of the total out-of-plane demagnetizationenergy of the free layer 130′″.

Thus, the magnetic elements 100, 100′, 100″, and 100′″ utilize freelayers having a high perpendicular anisotropy. Consequently, themagnetic elements 100, 100′, 100″, and 100′″ can be written using spintransfer at a lower switching current density. Furthermore, aspects ofthe magnetic elements 100, 100′, 100″, and 100′″ can be combined tofurther raise the perpendicular anisotropy. Thus, a further reduction incurrent or another improvement in the properties of the magneticelements 100, 100′, 100″, and/or 100′″ can be achieved.

FIG. 4 depicts a second embodiment of a magnetic element 200 inaccordance with the present invention having a reduced write currentdensity for spin transfer. The magnetic element 200 includes a spinvalve portion 204 and a spin tunneling junction portion 202 that share afree layer 230. The spin valve portion 204 includes a pinning layer 260that is preferably an antiferromagnetic (AFM) layer 260, pinned layer250, conductive spacer layer 240 such as Cu, and a free layer 230. In analternate embodiment, the conductive spacer layer 240 could be replacedby a barrier layer. The spin tunneling junction portion 202 includes apinning layer 206 that is preferably an antiferromagnetic (AFM) layer206, pinned layer 210, barrier layer 220 that is an insulator configuredto allow electrons to tunnel through it, and the free layer 230.Referring to FIGS. 2A and 4, the layers 250, 240, and 230 are analogousto the layers 110, 120, and 130 in the magnetic element 100 when thespacer layer 120 is conducting. Similarly, the layers 210, 220, and 230are analogous to the layers 110, 120, and 130, respectively, when thespacer layer 120 is an insulating barrier layer. The pinned layers 210and 250 thus preferably correspond to the pinned layers 110 and can beconfigured using analogous materials, layers, and/or process. Forexample, the pinned layer 210 and/or the pinned layer 250 may includemultilayer (Fe_(x)Co_(1-x)/Cu)n, where the n is the number of repeatsthat is greater than one. In addition, the Fe atomic percent, x, ispreferably approximately 0.5 and the Cu layers are preferably onethrough eight Angstroms thick. The free layer 230 is configured to bewritten using spin transfer and has a high perpendicular anisotropy.Moreover, the magnetic element 200 preferably utilizes two terminals(not shown) near the top and bottom of the magnetic element. However,nothing prevents the use of another number of terminals, for example athird terminal near the center of the magnetic element 200. The magneticelement 200 also includes pinning layers 206 and 260 that are preferablyAFM layers used in pinning the magnetizations of the pinned layers 210and 250, respectively.

The free layer 230 is preferably configured in a manner analogous to thefree layers 130, 130′, 130″, and/or 130′″. Thus, analogous materials andprinciples to those discussed above may be used to achieve the highperpendicular anisotropy of the free layer 230. Materials having a highcrystalline perpendicular anisotropy and/or other conditions such asstress could be used to achieve the high perpendicular anisotropy forthe free layer 230. In addition, as discussed above with respect to thefree layer 130′, the free layer 230 can be synthetic. Consequently, themagnetic element 200 can be written using spin transfer at a lowerswitching current density. Stated differently, the magnetic element 200can share the benefits of the magnetic elements 100, 100′, 100″, 100′″,and/or their combinations. Furthermore, when the pinned layers 210 and250 are aligned antiparallel, both the spin valve portion 204 and thespin tunneling junction portion 202 can contribute to writing the freelayer 230. Because of the use of the barrier layer 220, the magneticelement 200 has higher resistance and magnetoresistance. Consequently, ahigher signal may be obtained during reading.

FIG. 5A is a preferred version of the second embodiment of a magneticelement 300 in accordance with the present invention having a reducedwrite current density for spin transfer. The magnetic element 300 isanalogous to the magnetic element 200 depicted in FIG. 4. Thus,analogous components are labeled similarly. Therefore, the magneticelement includes a free layer 330, which corresponds to the free layer230, that has a high perpendicular anisotropy is written using spintransfer. Moreover, the magnetic element 300 preferably utilizes twoterminals (not shown) near the top and bottom of the magnetic element.However, nothing prevents the use of another number of terminals, forexample a third terminal near the center of the magnetic element.

The free layer 330 is preferably configured in a manner analogous to thefree layers 130, 130′, 130″, 130′″, and/or the free layer 230. Thus,analogous materials and principles to those discussed above may be usedto achieve the high perpendicular anisotropy of the free layer 330. Forexample, materials having a high crystalline perpendicular anisotropyand/or other conditions such as stress could be used to achieve the highperpendicular anisotropy for the free layer 330. Thus, the materialsdiscussed above with respect to the free layers 130, 130′, 130″, and130′″ are preferred. In addition, as discussed above with respect to thefree layer 130′, the free layer 330 can be synthetic. Because of thehigh perpendicular anisotropy, the magnetic element 300 can be writtenusing spin transfer at a lower switching current density. Stateddifferently, the magnetic element 300 can share the benefits of themagnetic elements 100, 100′, 100″, 100′″ and/or their combinations.Because of the use of the barrier layer 320, the magnetic element 300has higher resistance and magnetoresistance. Consequently, a highersignal may be obtained during reading. In an alternate embodiment, thebarrier layer 320 may be replaced by a conducting layer. However, insuch an embodiment, the read signal is decreased for a given readcurrent.

In the magnetic element 300, the pinned layer 310 is synthetic. Thepinned layer 310 thus includes ferromagnetic layers 312 and 316separated by a nonmagnetic layer 314, which is preferably Ru. Thenonmagnetic layer 314 is configured such that the ferromagnetic layers312 and 316 are antiferromagnetically aligned. Furthermore, the magneticelement 300 is configured such that the ferromagnetic layer 316 and thepinned layer 350 are antiparallel. As a result, the spin valve portion304 and the spin tunneling junction portion 302 can both contribute tothe spin transfer used to write to the magnetic element 300. Thus, aneven lower switching current can be used to write to the magneticelement 300. In addition, because adjacent layers 312 and 350 have theirmagnetizations aligned parallel, the AFM layers 306 and 360 can bealigned in the same direction. The AFM layers 306 and 360 can,therefore, be aligned in the same step. Thus, processing is furthersimplified.

The free layers 230 and 330, as well as the magnetic elements 200 and300, can be configured in an analogous manner to that discussed above.For example, FIG. 5B depicts another version of the second embodiment300′ of a portion of a magnetic element in accordance with the presentinvention having a reduced write current density for spin transfer dueto at least a high perpendicular anisotropy. The magnetic element 300′is analogous to the magnetic element 300 and, therefore, shares itsadvantages. For example, the free layer 330′ has a high perpendicularanisotropy. Furthermore, in a manner similar to the magnetic element100″, the magnetic element 300′ includes stress increasing layer 380that is analogous to the stress increasing layer 154. Although only thestress increasing layer 380 is depicted, another stress increasing layercould be used between the free layer 330′ and the barrier layer 320′.However, such a layer would strongly reduce the tunnelingmagnetoresistance because this layer would lie adjacent to the barrierlayer 320′. With the use of the stress increasing layer 380 and/or, inan alternate embodiment, a stress increasing layer between the freelayer 330′ and the barrier layer 320′, the high perpendicular anisotropyof the free layer 330′ may be obtained. Thus, the benefits of themagnetic element 100″ may also be achieved.

FIG. 5C depicts a third version of the second embodiment of a portion ofa magnetic element 300″ in accordance with the present invention havinga reduced write current density for spin transfer due to at least a highperpendicular anisotropy. The magnetic element 300″ is analogous to themagnetic element 300 and, therefore, shares its advantages. For example,the free layer 330″ has a high perpendicular anisotropy. Furthermore, ina manner similar to the magnetic element 100′″, the magnetic element300″ includes very high perpendicular anisotropy ferromagnetic layer 390that is preferably analogous to the very high perpendicular anisotropyferromagnetic layer 160 depicted in FIG. 3B and a high spin polarizationferromagnetic layers 391 and 393 analogous to the high spin polarizationlayer 162. Thus, the very high perpendicular anisotropy ferromagneticlayer 390 is preferably a rare earth-transition metal alloy.Furthermore, the thicknesses of the very high perpendicular anisotropyferromagnetic layer 390 and the ferromagnetic layers 391 and 393 arepreferably tailored such that the equilibrium magnetizations of the veryhigh perpendicular anisotropy ferromagnetic layer 390 and theferromagnetic layers 391 and 393 are in plane, as depicted. Thus, thehigh perpendicular anisotropy of the free layer 330″ that is analogousto the free layer 130′″ may be achieved. Consequently, the benefits ofthe magnetic element 100′″ may also be attained.

In an alternative embodiment, the very high perpendicular anisotropyferromagnetic layer 390 can include multilayers [Co/Pd]n/Co,[Co/Pt]n/Co, [CoFe/Pd]n/CoFe, [CoFe/Pt]n/CoFe, [CoCr/Pd]n/CoCr, or[CoCr/Pt]n/CoCr where n is between 1 and 10, Co 3 A to 20 A, CoFe 3 A to20 A, CoCr 3 A to 20 A, Pd 10 A to 100 A, Pt 10 A to 100 A. The repeatnumber n and the exact thicknesses of Co, CoFe, CoCr, Pd, and Pt arechosen so that the total perpendicular anisotropy energy is betweentwenty and ninety five percent of the total out-of-plane demagnetizationenergy of the free layer 330″.

FIG. 6 depicts a third embodiment of a portion of a magnetic element 400in accordance with the present invention having a reduced write currentdensity for spin transfer. The magnetic element includes two structures402 and 404, each of which is analogous to the magnetic element 100,100′, 100″, and/or 100′″. Thus, the structure 402 includes a pinnedlayer 410, a spacer layer 420, and a free layer 430 that are analogousto, for example, the layers 110, 120, and 130, respectively, of themagnetic element 100. The structure 402 also includes pinning layer 406that is preferably an AFM layer. Similarly, the structure 404 includes apinned layer 470, a spacer layer 460, and a free layer 450 that areanalogous to, for example, the layers 110, 120, and 130, respectively,of the magnetic element 100. The structure 404 also includes pinninglayer 480 that is preferably an AFM layer. One or both of the freelayers 430 and 450 have a high perpendicular anisotropy. The free layer430 and/or 450 may also be synthetic. In such a case the ferromagneticlayers (not explicitly shown) within the free layer 430 and/or 450 wouldhave a high perpendicular anisotropy. Furthermore, the free layers 430and 450 of the magnetic element 400 are magnetostatically coupled,preferably so that the layers 430 and 450 are antiferromagneticallyaligned. In the embodiment shown, the magnetic element 400 includes aseparation layer 440. The separation layer 440 is configured to ensurethat the free layers 430 and 450 are only magnetostatically coupled. Forexample, the thickness of the separation layer 440, which is preferablya nonmagnetic conductor, is preferably configured to ensure that thefree layers 430 and 450 are antiferromagnetically aligned due to amagnetostatic interaction. In particular, the separation layer 440serves to randomize the polarization of the spins passing through it.For example, the separation layer 440 includes materials such as Cu, Ag,Au, Pt, Mn, CuPt, CuMn, a Cu/Pt[1-20 A]/Cu sandwich, a Cu/Mn[1-20 A]/Cusandwich, or a Cu/PtMn[1-20 A]/Cu sandwich. Although the separationlayer is used in the magnetic element 400, nothing prevents anothermechanism from being used. For example, in one embodiment, the structure402 might be a dual structure including a second pinned layer (notshown), a second spacer layer (not shown), and a pinning layer (notshown). The thicknesses of the second pinned and spacer layers, as wellas the pinning layer may be configured to ensure that the free layers430 and 450 are magnetostatically coupled.

The free layer 430 and/or the free layer 450 are configured to have ahigh perpendicular anisotropy, as defined above. Thus, the free layer430 and/or 450 may correspond to the free layers 130, 130′, 130″, and/or130′″. Stated differently, the materials and/or properties used in thefree layer 430 and/or the free layer 450 are the same as or analogous tothose described above with respect to the magnetic elements 100, 100′,100″, and 100′″. Thus, the magnetic element 400 shares many of thebenefits of the magnetic elements 100, 100′, 100″, and 100′″. Inparticular, the magnetic element can be written using spin transfer at alower switching current density.

The magnetostatic coupling between the free layers 430 and 450 providesfurther benefits. Because the free layers 450 and 430 aremagnetostatically coupled, a change in magnetization of the free layer450 is reflected in the free layer 430. The spacer layer 420 can beeither a conductive layer or a barrier layer that provides a highsignal. Furthermore, because they have separate free layers 450 and 430the properties of the spin valve 404 and the spin tunneling junction402, respectively, can be separately tailored to improve their functionsof the spin valve and spin tunneling junction, respectively.

FIG. 7A is a preferred version of the third embodiment of a magneticelement 500 in accordance with the present invention having a reducedwrite current density for spin transfer. The magnetic element 500 isanalogous to the magnetic element 400 depicted in FIG. 6. Thus,analogous components are labeled similarly. Therefore, the magneticelement includes free layers 530 and 550, which corresponds to the freelayers 430 and 450, respectively, either or both of which has a highperpendicular anisotropy and both of which are written using spintransfer. The free layer 530 and/or 550 may also be synthetic. In such acase the ferromagnetic layers (not explicitly shown) within the freelayer 530 and/or 550 would have a high perpendicular anisotropy.Moreover, the magnetic element 500 preferably utilizes two terminals(not shown) near the top and bottom of the magnetic element. However,nothing prevents the use of another number of terminals, for example athird terminal near the center of the magnetic element 500.

The pinned layers 510 and 570 are synthetic. Thus, the pinned layer 510includes ferromagnetic layers 512 and 516 separated by a nonmagneticlayer 514 that is preferably Ru. The magnetizations of the ferromagneticlayers 512 and 516 are also aligned antiparallel. Similarly, the pinnedlayer 570 includes ferromagnetic layers 572 and 576 separated by anonmagnetic layer 574 that is preferably Ru. The magnetizations of theferromagnetic layers 572 and 576 are also aligned antiparallel.Furthermore, the spacer layer 520 is preferably a barrier layer that isinsulating yet allows electrons to tunnel between the ferromagneticlayer 516 and the free layer 530. The spacer layer 560 is preferably aconductive layer. Thus, the structure 502 is a spin tunneling junction,while the structure 504 is a spin valve.

The free layers 530 and/or 550 are preferably configured in a manneranalogous to the free layers 130, 130′, 130″, 130′″, and/or the freelayers 430 and 450, respectively. Thus, analogous materials andprinciples to those discussed above may be used to achieve the highperpendicular anisotropy of the free layers 530 and/or 550. For example,materials having a high crystalline perpendicular anisotropy and/orother conditions such as stress could be used to achieve the highperpendicular anisotropy for the free layer 530 and/or 550. Thus, thematerials discussed above with respect to the free layers 130, 130′,130″, and 130′″ are preferred. In addition, as discussed above withrespect to the free layer 130′, the free layers 530 and/or 550 can besynthetic. Because of the high perpendicular anisotropy, the magneticelement 500 can be written using spin transfer at a lower switchingcurrent density. Stated differently, the magnetic element 500 can sharethe benefits of the magnetic elements 100, 100′, 100″, 100′″, and/ortheir combinations.

Furthermore, because the free layers 530 and 550 are magnetostaticallycoupled, a change in magnetization direction of the free layer 550, forexample due to spin transfer induced writing, is reflected in themagnetization of the free layer 530. With the barrier layer 520, thespin tunneling junction 502 provides a high signal. In an alternateembodiment, the barrier layer 520 may be replaced by a conducting layer.However, in such an embodiment, the read signal is decreased for a givenread current.

As previously mentioned, the free layers 530 and 550, as well as themagnetic element 500, can be configured in an analogous manner to thatdiscussed above. For example, FIG. 7B is another version of the thirdembodiment of a magnetic element 500′ in accordance with the presentinvention having a reduced write current density for spin transfer dueto at least a high perpendicular anisotropy. The magnetic element 500′is analogous to the magnetic element 500 and, therefore, shares itsadvantages. For example, the free layers 530′ and/or 550′ have a highperpendicular anisotropy. Furthermore, in a manner similar to themagnetic element 100″, the magnetic element 500′ includes optionalstress increasing layers 582, 584 and 586 that are analogous to theoptional stress increasing layers 152 and 154. The bottom, the top, orboth of the optional stress increasing layers 582, 584, and 586 may beused. Although not depicted, an optional stress increasing layer couldbe placed between the free layer 530′ and the barrier layer 520′.However, such an optional stress increasing layer may result in a lowermagnetoresistance. In addition, use of the optional stress increasinglayer 586 may result in a lower spin torque for spin transfer as well asa lower magnetoresistance for the spin valve 504′. Thus, the highperpendicular anisotropy of the free layer 530′ and/or 550′ may beobtained. Thus, the benefits of the magnetic element 100″ may also beachieved.

FIG. 7C depicts a third version of the second embodiment of a portion ofa magnetic element 500″ in accordance with the present invention havinga reduced write current density for spin transfer due to a highperpendicular anisotropy. The magnetic element 500″ is analogous to themagnetic element 500 and, therefore, shares its advantages. For example,the free layer 530″ and/or 550″ have a high perpendicular anisotropy.Furthermore, in a manner similar to the magnetic element 100′″, the freelayer(s) 530″ and 550″ include very high perpendicular anisotropyferromagnetic layer(s) 590 and 591, respectively, that are preferablyanalogous to the very high perpendicular anisotropy ferromagnetic layer160 depicted in FIG. 3B. The free layer(s) 530″ and 550″ also includeferromagnetic layers 592 and 593 having a high spin polarization.Additionally, a seed layer, such as AlCu 25 nm, can be optionallyinserted between layers 540″ and 591 to help enhance the perpendicularanisotropy of layer 591. Furthermore, the thicknesses of the very highperpendicular anisotropy ferromagnetic layer(s) 590 and 591 and theferromagnetic layer(s) 592 and 593, respectively, are preferablytailored such that the equilibrium magnetizations of the very highperpendicular anisotropy ferromagnetic layer(s) 590 and 591 and theferromagnetic layer(s) 592 and 593 are in plane, as depicted. Thus, thevery high perpendicular anisotropy ferromagnetic layers 590 and 591 arepreferably a rare earth-transition metal alloy.

Alternatively, the very high perpendicular anisotropy ferromagneticlayer(s) 590 and 591 can be multilayers [Co/Pd]n/Co, [Co/Pt]n/Co,[CoFe/Pd]n/CoFe, [CoFe/Pt]n/CoFe, [CoCr/Pd]n/CoCr, or [CoCr/Pt]n/CoCrwhere n is between 1 and 10, Co 3 A to 20 A, CoFe 3 A to 20 A, CoCr 3 Ato 20 A, Pd 10 A to 100 A, Pt 10 A to 100 A. The repeat number n and theexact thicknesses of Co, CoFe, CoCr, Pd, and Pt are chosen so that thetotal perpendicular anisotropy energy is between twenty and ninety fivepercent of the total out-of-plane demagnetization energy of the freelayer 530″ and/or 550″. Thus, the high perpendicular anisotropy of thefree layer 530″ and/or 550″ may be achieved. Consequently, the benefitof the magnetic element 100′″ may also be provided.

Thus, the magnetic elements 100, 100′, 100″, 100′″, 200, 300, 300′,300″, 400, 500, 500′, and 500″ can be written using spin transfer at alower switching current density due to high perpendicular anisotropyand/or low saturation magnetization in at least one free layer.Furthermore, aspects of the magnetic elements 100, 100′, 100″, 100′″,200, 300, 300′, 300″, 400, 500, 500′, and 500″ can be combined toprovide further benefits.

FIG. 8 depicts a flow chart of a one embodiment of a method 600 inaccordance with the present invention for providing one embodiment of amagnetic element in accordance with the present invention having areduced write current density for spin transfer. The method 600 isdescribed in the context of the magnetic element 100. However, nothingprevents the method 600 from being adapted to provide the magneticelements 100′, 100″, 100′″, 200, 300, 300′, 300″, 400, 500, 500′, and/or500″. A pinned layer, such as the pinned layer 110 is provided, via step602. In one embodiment, step 602 includes providing a synthetic pinnedlayer. The spacer layer 120 is provided, via step 604. Step 604 caninclude providing a barrier layer or a conducting layer. The free layer130 having a high perpendicular anisotropy is provided, via step 606. Insome embodiments, the very high perpendicular anisotropy ferromagneticlayer or the stress inducing layer may be provided prior to step 606.Step 606 can include providing a synthetic free layer. In such anembodiment, step 606 may also include providing high spin polarizationlayers between the ferromagnetic layers of the free layer. If themagnetic elements 200, 300, 300′, 300″, 400, 500, 500′, and/or 500″ arebeing provided, additional pinned layers, spacer layers and, in someembodiments, free layers are provided, via step 608. In suchembodiments, the free layers may have a high perpendicular anisotropy.Thus, the magnetic elements 100′, 100″, 100′″, 200, 300, 300′, 300″,400, 500, 500′, and/or 500″ may be provided.

A method and system has been disclosed for providing a magnetic elementthat can be written using spin transfer at a lower switching currentdensity. Although the present invention has been described in accordancewith the embodiments shown, one of ordinary skill in the art willreadily recognize that there could be variations to the embodiments andthose variations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

1. A magnetic element comprising: a pinned layer; a spacer layer, thespacer layer being nonmagnetic; and a free layer having a free layermagnetization, the spacer layer residing between the pinned layer andthe free layer, the free layer including a first ferromagnetic layer anda second ferromagnetic layer, the second ferromagnetic layer having avery high perpendicular anisotropy and an out-of-plane demagnetizationenergy, the very high perpendicular anisotropy energy being greater thanthe out-of-plane demagnetization energy; wherein the magnetic element isconfigured to allow the free layer magnetization to be switched due tospin transfer when a write current is passed through the magneticelement.
 2. The magnetic element of claim 1 wherein the firstferromagnetic layer resides between the spacer layer and the secondferromagnetic layer.
 3. The magnetic element of claim 1 wherein thespacer layer is an insulating barrier layer.
 4. The magnetic element ofclaim 1 wherein the spacer layer is conductive.
 5. The magnetic elementof claim 1 wherein the first ferromagnetic layer has a high spinpolarization.
 6. The magnetic element of claim 5 wherein the firstferromagnetic layer includes at least one of Co, Fe and CoFe
 7. Themagnetic element of claim 6 wherein the spacer layer is an insulatingbarrier layer.
 8. The magnetic element of claim 6 wherein the spacerlayer is conductive.
 9. The magnetic element of claim 5 wherein thefirst ferromagnetic layer is exchanged coupled with the secondferromagnetic layer.
 10. The magnetic element of claim 6 wherein thesecond ferromagnetic layer has an out-of-plane magnetization.
 11. Themagnetic element of claim 6 further comprising: an additional pinnedlayer; and an additional spacer layer, the additional spacer layerresiding between the additional pinned layer and the free layer.
 12. Themagnetic element of claim 11 further comprising: an additional freelayer residing between the additional spacer layer and the free layer.13. The magnetic element of claim 12 wherein the additional free layerfurther includes a third ferromagnetic layer and a fourth ferromagneticlayer, the fourth ferromagnetic layer having a very high perpendicularanisotropy and an out-of-plane demagnetization energy, the very highperpendicular anisotropy energy being greater than the out-of-planedemagnetization energy.
 14. The magnetic element of claim 1 furthercomprising: an additional pinned layer; and an additional spacer layer,the additional spacer layer residing between the additional pinned layerand the free layer.
 15. The magnetic element of claim 14 furthercomprising: an additional free layer residing between the additionalspacer layer and the free layer.
 16. The magnetic element of claim 15wherein the additional free layer further includes a third ferromagneticlayer and a fourth ferromagnetic layer, the fourth ferromagnetic layerhaving an additional very high perpendicular anisotropy and anadditional out-of-plane demagnetization energy, the additional very highperpendicular anisotropy energy being greater than the additionalout-of-plane demagnetization energy.